The present invention relates to a method and system for an in situ or non-invasive vibro-acoustic (VA) analysis of an arbitrary machine.
Currently, structural vibration analysis is primarily done by using modal analysis, which is used to identify the natural frequencies, natural modes and damping ratios of a system. With this information, engineers may be able to suppress structural vibrations and improve the performance of a machine. Such a technique has been employed by vibration engineers for many years and has been documented extensively in the literature.
Traditional vibration modal analysis is suitable for simple structures with simple boundary conditions subject to simple excitations; however, there are many inherent difficulties in this approach. For example, it cannot handle cases in which modal overlapping occurs, namely, many natural modes occur at the same frequency. It does not allow for an in situ or non-invasive vibration analysis of a machine running under its natural working condition. Oftentimes, one has to stop a machine, detach it from its original mounting unit, and place it in a special test set up. If a machine is too complicated, one has to disassemble it to facilitate modal analyses on individual components. Thus, instead of analyzing overall vibration behavior of a machine as a whole under its original operating condition, one must study individual components under entirely differently boundary conditions subject to different excitations. The reason for that is because modal analysis relies on measurements of transfer functions (TF) between an excitation force and responses. When a machine runs on its own, for example, a fired engine, there is no way to measure the excitation (combustion) forces that occur inside the cylinders of this engine. Most importantly, traditional modal analysis is for structural vibration only. It has nothing to do with sound radiation into the surrounding medium. Therefore, results cannot be used to guide design modification to suppress sound.